The London museum has overcrowded galleries and needs more space — even though it barely has the money to maintain its current facilities

When the Tate Modern opened here 10 years ago, it was the first national museum built in Britain in 100 years and the first museum in London devoted solely to modern art. A hulking brick building that was a former power station on the south side of the Thames River at Bankside, a slowly gentrifying area just opposite St Paul’s Cathedral, the US$208 million museum captivated the art world and made a city better known for its stuffier, historic collections into an international mecca for new art.

Forty-five million people have been through the galleries of the Tate Modern since its opening, more than twice the number officials had predicted. Now Nicholas Serota, director of all the Tate museums (a network that includes Tate Britain across the river in Millbank as well as branches in Liverpool and St Ives) and the mastermind behind the Tate Modern, insists that despite the rocky economy and the recent announcement of government cutbacks for arts financing, the Tate Modern must grow.

A victim of its own success, the museum has overcrowded galleries, he explained, and needs not just more space but also different kinds of spaces. This spring it broke ground on an extension next to the existing building on a plot of land with disused oil tanks that once held fuel to power London. Under construction is an 11-story glass-and-perforated-brick origamilike structure by Swiss architects Herzog & de Meuron, who transformed the power station into the Tate Modern.

“Of course it’s a tough time,” Serota said one summer morning sitting sipping tea in his office across the river at Tate Britain. “But it’s not the moment to give up. Some of the great museums in America were built during a depression.”

On a cloudless afternoon a few days later, the grounds around the Tate Modern were packed. Families were picnicking on its lawn beside the banks of the Thames; crowds were hanging around Turbine Hall, the museum’s cavernous main entrance; and people were clustered inside the galleries, many glued to the video screens of A Story of Deception, a major exhibition devoted to Francis Alys, a Mexico City artist known for politically charged work. But unlike most US museums, which feel spic and span, the Tate Modern seems worn out.

Visitors have not been kind to the building. When it opened, officials said they expected 2 million to 2.5 million people the first year. More than 5 million came. Now attendance hovers around 4.5 million people a year. (By way of comparison, the Museum of Modern Art in New York reports that its attendance last year was about 3 million, a record for the institution.) The Tate Modern’s galleries have taken a beating. Some look as though they could use fresh paint; the bathrooms are dirty; and during rush hour the cafes seem chaotic.

“I think it’s better than it was,” Serota said. “Frankly we were overwhelmed when we first opened. To go from zero to 5 million visitors in one year is asking a lot. And I think that years two and three the institution was to some extent struggling with its own success. But it’s now grown to a place where it seems comfortable.”

The extension was part of the Tate Modern’s original plan, Serota was quick to point out. (Crews are working daily, and the museum’s Web site, tate.org.uk/modern/transformingtm/today.htm, offers a live feed from the site, updated every 15 minutes.)